N.m.r., e.p.r. and magnetic-c.d. studies of cytochrome f. Identity of the haem axial ligands.

N.m.r.-, magnetic-c.d.- and e.p.r.-spectroscopic studies of oxidized and reduced cytochrome f from charlock, rape and woad are reported. Comparison of the spectra with corresponding spectra of other haem proteins, including horse and yeast cytochromes c, bovine cytochrome b5 and n-butylamine adduct of soya-bean leghaemoglobin support the hypothesis [Siedow, Vickery & Palmer (1980) Arch. Biochem. Biophys. 203, 101-107] that lysine is the sixth ligand of native cytochrome f. Detailed analysis of the e.p.r. spectrum of ferricytochrome f indicates that its principle g-values are 3.51, 1.70 and less than 1.3, and not 3.48, 2.07 and 1.6 as previously suggested [Siedow, Vickery & Palmer (1980) Arch. Biochem. Biophys. 203, 101-107]. The observation of a one-proton intensity resonance at -3.27 p.p.m. in the 1H-n.m.r. spectrum of ferrocytochrome f, coupled with the absence of a methionine methyl resonance from the spectral region to low frequency of -2 p.p.m., is suggested to be a general indicator of lysine co-ordination.